In heating the interiors of buildings, several conventional heating methods have been employed, including hot water/steam and forced air heating. Generally, these heating methods require the installation of large air ducts or extensive water piping, both of which take up a considerable amount of space within a building and require careful planning for locations of vents, radiators, and so forth. Vents and ducts tend to obstruct living and working areas within a building and require other components of the building (ceilings, walls, etc.) to be designed around them. Some hot water systems include piping which is embedded in a flooring or ceiling material through which warm water is circulated to heat a building. In some geographic localities, however, electrical power is cheaper than gas, and direct electric heating is desired.
Electric heating cables have been employed to heat cement slabs and the like by being positioned in a sand layer beneath the slabs. High limit switches have been employed adjacent the cables to sense the cable temperatures and to prevent the cables from-overheating. Temperature sensors imbedded in the concrete slabs regulate the electric current supplied to the heating cable, therefore being regulated room heat by controlling the temperature of the concrete beneath which, embedded in sand, were the electric heating cables. Positioning the temperature sensors in the room air space above the flooring resulted in prohibitively long response times.